1. Field of the Invention
The present invention relates to a broadcast recording system for recording broadcast contents for time-shift viewing. More particularly, the present invention relates to technology for reducing the storage space of a recording medium used to record the contents.
2. Description of the Related Art
In addition to real-time viewing, viewers of TV broadcasts are allowed to record contents with a recording apparatus for the purpose of time-shift viewing at their convenience.
JP Translation of International Application Publication No. 2002-521978 (page 13, FIG. 1) discloses technology for recording contents to a recording medium such as a hard disk in digital form and for playback of recorded contents.
FIG. 1 is a view showing the structure of a conventional recording apparatus 100. The recording apparatus 100 is composed of functional blocks of a receiving unit 101, a switch 102, an output unit 103, a hard disk 104, and a CPU 105.
The receiving unit 101 converts received contents to MPEG2 (Moving Picture Experts Group phase 2) streams, and outputs the resulting MPEG2 streams. For example, when video input is an analog signal according to the NTSC (National Television System Committee) standard, a tuner provided in the receiving unit 101 tunes for a target content, and an MPEG encoder, that is also provided in the receiving unit 101, converts the content to an MPEG2 stream and outputs the resulting stream. In another example, when video input is a digital signal is an MPEG2 transport stream (hereinafter simply referred to as TS) multiplexed with an MPEG2 stream containing a content, a digital tuner provided in the receiving unit 101 extracts a target MPEG2 stream from the inputted TS, and outputs the extracted MPEG2 stream.
The switch 102 receives, in recording operations, a content to be recorded from the receiving unit 101 and outputs the content to the hard disk 104. In playback operations, the switch 102 reads a content to be played back from the hard disk 104 and outputs the read content to the output unit 103.
The output unit 103 acquires an MPEG2 stream and outputs the acquired MPEG2 stream to a television set connected to the recording apparatus 100. In the case where the television set is in compliance with the NTSC standard, the output unit 103 outputs the content after decoding it to an NTSC signal.
The hard disk 104, in recording operations, records an MPEG2 stream inputted from the switch 102 to a storage area. In playback operations, the hard disk 104 reads an MPEG2 stream that corresponds to a content requested for playback, and outputs the read MPEG2 stream to the switch 102.
The CPU 105 controls operations of the receiving unit 101, the switch 102, the output unit 103, and the hard disk 104 in order to carryout recording or playback of a requested content according to a user operation or to a recording schedule programmed in advance by the user. When recoding of a content is requested by a user operation or a programmed recording schedule, the CPU 105 controls overall operations, so that the receiving unit 101 acquires the requested content, the switch 102 outputs the MPEG2 stream inputted from the receiving unit 101 to the hard disk unit 104, and the hard disk 104 records the inputted MPEG2 stream.
When playback of a content is requested by a user operation, the CPU 105 controls overall operations, so that the hard disk 104 reads an MPEG2 stream corresponding to the requested content, the switch 102 outputs the MPEG2 stream inputted from the hard disk 104 to the output unit 103, and the output unit 103 decodes the inputted MPEG2 stream to audio and video signals and then outputs the resulting signals to an external television set. There may be a case where the recording apparatus is requested to carry out playback of a content recorded in the hard disk 104 while recording another content. In this case, the CPU 105 controls the recording and the playback in parallel, so that the switch 102 outputs an MPEG2 stream inputted from the receiving unit 101 to the hard disk unit 104, and concurrently outputs an MPEG2 stream inputted from the hard disk 104 to the output unit 103.
The recording apparatus having the above-stated structure is capable of recording a content requested by a user, and playback of a recorded content any time at user's convenience.
Recently, recording apparatuses with a large-capacity recording medium such as a hard disk and a DVD-RAM are now in common use. Such a recording apparatus is capable of recording contents in digital form, which is bulky but of high image quality. Users of those recording apparatuses tend to record a number of contents for the purpose of time-shift viewing. In order to meet the users' demand for recording a large number of contents, it is desired to increase the storage capacity of recording apparatuses.
Unfortunately, however, increase in the storage capacity inevitably involves increase in the cost. Yet, it is undesirable to record contents at higher data compression ratio, which leads to another problem of degradation in image quality.